Obito had thought he had been the luckiest boy in the world.
He and Rin found each other early and became pack mates at a very young age. They were best friends, inseparable, and knew each other like the back of their hands. And even better, Obito had found his mate at a young age! Well, Rin did, but it still counted. Okay, his mate was a know-it-all asshole who was too smug for his own good, and should have been born an Uchiha for all the smugness he produced. But Kakashi was cute, in his own tiny, bossy way. So while Obito argued with the jerk a lot, he loved him anyway. The Omega was his mate after all, he had known that the first time their eyes had met.
People are born with their secondary gender already within them, but they don't awaken their other half until they met their mate, and even then they still aren't officially an adult. No, they had to wait for their rut or heat, if they were an Alpha or Omega.
Aunt Mikoto had told him how she felt when she met Fugaku for the first time at twelve years old. The moment she had met his eyes her Omega stirred from her slumber and cried in joy, demanding they kiss Fugaku. Fugaku of course tried to kiss her, lost in his Alpha, but before either of them could, Aunt Mikoto's red headed team mate booted Fugaku into next week.
Aunt Mikoto ended up laughing at her poor mate even as she helped him out of a wall.
The same thing happened to Obito.
Minus the being kicked into a wall. He was very glad that didn't happen.
His Alpha had yelled in delight when they met Kakashi properly, calling for 'their Omega'. Obito's ears had ached at how loud his Alpha was.
Rin had been smug for weeks.
She had been the one to set up the 'play date' of kick the can after all. The Beta had somehow known that he and Kakashi were mates.
Rin was beautiful and clever in every way, and had been the one to bring them together. Obito loved her for that. She always held a special place in his heart for finding his mate so early in his life. He vowed to find her mate for her in return.
Obito was a lucky Alpha.
Obito had been a mad, excitable thing all day long after he had met Kakashi. The six year old had talked everyone in the Clan's ears off about how cute and tiny his four year old mate was, bouncing around, laughing and beaming wildly.
Obito had even ran to where he knew his Aunt Mikoto was reuniting with her team mates. Her red headed friend had been there, along with their sensei. Obito couldn't recall who their last team mate was. He had never met them in fact, and when Obito finally asked, Aunt Mikoto grew sad and distant, while Fugaku grew angry. The Alpha had hugged Mikoto close, after slapping the back of Obito's head roughly.
Obito never asked again.
When he told his aunt about his mate she had cooed and pinched his cheek, teasing him relentlessly. Her friend and teammate Kushina happily joined in. Kushina was so annoying, but luckily Obito rarely had to deal with her.
Their Sensei, the Legendary White Fang, (who always made Obito squeal in delight, because by Kami it was the White Fang of Konoha,) looked amused the entire time he described his mate, his grumpy Omega. Obito had completely missed the knowing looks that passed between the three of teammates, far too absorbed in his own excitement.
Obito was a lucky Alpha.
Except it all went wrong one day when Kakashi disappeared from school. It took a week for him to come back and he had grown cold and distant.
Suddenly Kakashi didn't want him around anymore, nor Rin, despite how much fun they had playing and training together. Kakashi ruthlessly completed his school work and left them behind in the dust, graduating from school to become a Genin at five.
Aunt Mikoto grew quiet and distant around the same time, and Obito had caught her punching someone in the streets, eyes burning red, after the Alpha had made a comment about the White Fang.
The Alpha had been sent to hospital after that one punch, all while Fukgaku struggled to drag Aunt Mikoto away when she began to draw her sword.
She rarely left the Uchiha Estate after that.
Kushina's, Aunt Mikoto's old team mate's, reputation for being a violent hothead grew worse that year. There were rumours of her destroying bars and beating people bloody.
Okay, things went a little wrong, but Obito was still a lucky Alpha.
Kakashi never warmed up to them again, no matter how much he and Rin tried. The only one who seemed to get through the coldness was Pakkun, but he was Kakashi's pack. Him and all Kakashi's ninken. They didn't count. Kakashi needed his mate.
Obito needed him too. His Alpha was sad and lonely and he didn't like it. It made Obito feel horrible.
Finally Obito graduated at nine, early due to the war, but by that point Kakashi was a Chunin who had been taught by Minato Sensei for a few years. The Alpha was kind, but his mate was annoying. Kushina was the worst Omega ever. Obito was a good and strong Alpha, not some little kid. She was such a pest.
Obito was lucky. Things were back to where they should be.
It felt amazing to have Kakashi and Rin at his side again. His mate and his best friend. Rin was just as delighted, and they had both noticed Kakashi soften, by just the smallest touch. It had lifted Obito's spirits.
But then Kannabi Bridge happened.
Kakashi became a Jonin at twelve. Still a pup! Not even gone through his first heat yet-
Obito learned what happened to the White Fang of Konoha. He learned exactly why Kakashi grew so cold and distant. Why Aunt Mikoto disliked speaking to people outside of her friends, and why Kushina's temper had grown even worse. Kakashi's father had saved his comrades, failing a mission to do so, and everyone had blamed Sakumo Hatake for it. Even those he had saved.
In the end being vilified by Konoha grew too much, and he took his own life.
Obito realised he wasn't as lucky as he thought. No, if he was then his Omega wouldn't have suffered so much.
Minato Sensei left them behind to go to the front lines, leaving Kakashi in charge. Rin was captured, and Kakashi said they needed to finish the mission. Obito nearly hit his mate, but his Alpha stopped him, stopped him from raising his fist. No, instead Obito charged off after Rin. But not before grabbing his mate and telling Kakashi what he really thought.
Obito was alone, then Kakashi came back. Kakashi lost his eye protecting him and Obito finally gained his Sharingan. He could finally help Kakashi. They managed to save Rin, but the enemy collapsed the cave on top of them. Kakashi nearly died due to his injury (the injury he got protecting Obito's reckless ass), but Obito caught him and threw him out the way of the boulders.
Obito left Kakashi behind with a gift, and an apology to Rin.
He didn't keep his promise to find her mate. Kakashi would have to do it instead on Obito's behalf. That was fine though. Kakashi and Rin were safe.
He died scared, blind and lonely, but relieved.
Then he didn't actually die. Madara Uchiha saved him.
And Obito realised that this world was Hell, and that he wasn't the luckiest boy in the world.
Rin committed suicide. She committed suicide using Kakashi. She had died to protect Konoha.
Fucking Konoha.
He realised anything could be taken away from him in a blink of an eye. Like Kakashi's father, and Obito's parents, and his best friend's life-
Obito was going to make the perfect world. He was going to make a world where his heart hadn't been ripped out of his chest after Rin's death. He was going to make a world where his Omega, his Kakashi, wouldn't be traumatised and throwing himself into mission after mission, trying to get himself killed while 'doing his duty for Konoha'. And Rin, their teammate, their friend, Obito's best friend, would live. She would get to grow old with them and have her own mate, and they'd all live happily with no more suffering.
Kakashi wouldn't spend his days haunting graves. Looking at the same names, over and over again.
Rin Nohara. Obito Uchiha. Sakumo Hatake. Rika Hatake.
Sakumo's and Rika's graves weren't even in the graveyard. Kakashi had to move them back to the Hatake Estate.
White Zetsu told him that people kept vandalising it during the war, so Kakashi had to move it. Then Konoha's people went after Rika Hatake's grave, so Kakashi had to move that too.
The thought had made Obito's blood boil.
People weren't safe even in death.
That's how badly this world needed saving from itself.
And he would save it.